#include <Keypad.h>
const byte ROWS = 4; 
const byte COLS = 4; 

char keys[ROWS][COLS] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};

byte rowPins[ROWS] = {5,4,3,2};
byte colPins[COLS] = {A0,A1,A3,A4};
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup()
{
  Serial.begin(9600); 
}

void loop()
{
  char key = keypad.getKey(); 
  if (key) 
  {
    Serial.println(key); 
  }
}